There is a general need to provide covering over open areas to provide protection from the rain and/or shade from the sun, so that people can enjoy the open air without being inconvenienced by the weather. It is commonplace to use retractable covers, for example, to cover small seating areas outside restaurants, private gardens and patios. However, covering larger areas of these examples and others such as children's play areas or campgrounds, outdoor swimming pools, amphitheaters and stadiums, with a retractable cover requires an entirely different system to those in existence. It is particularly desirable that such a covering system can be easily and quickly erected and dismantled to suit the particular weather conditions, thus causing minimum disruption to the users. It is also desirable for a single covering system to be able to cover a large area, so that it is not necessary to use a number of smaller systems in combination (which may not only be less visually attractive but also less effective and more inconvenient to assemble).
Another situation that requires the use of large covered areas is agriculture. Some plantations, fields or vineyards are covered by nets, plastic sheeting etc. to provide protection and preferential cultivation conditions for the crops.
A number of covering systems are known in the art. Some systems are free-standing and others require attachment to a building or a vehicle. U.S. Pat. No. 5,441,068 discloses a sunshade having a column that can be anchored to the ground. A number of arms spaced around the column support a sunshade membrane in the open position, and can be folded down adjacent the column to remove the shade as desired. U.S. Pat. No. 5,960,806 also discloses a free-standing sunshade. However, a disadvantage with umbrella-like sunshades is that these systems need a strong and thus often bulky and unattractive base, that usually has to feature at or near the centre of the covered area. Furthermore, these shades tend to be relatively small and thus many may be required to cover a large area.
Another type of covering system utilises a rolled cover that may be extended over the desired area.
U.S. Pat. No. 5,924,465 is an example of such an awning system for a vehicle. It comprises an awning rolled on a tube, arms extending from the side of the vehicle to support each side of the awning, a bracket connected between a side arm and the base of the vehicle to support the side arm, and a post resting on the ground to support a side arm. The awning can be unrolled and the various support members put in place, and then retracted and dismantled as necessary.
U.S. Pat. No. 6,494,246 also describes a retractable awning, that may be attached to a vehicle or building. The awning is unrolled from a roller tube. One end is fixed to a structure (vehicle or building) and the far end connected to the roller tube is supported by brackets extending at an angle between the roller tube and a lower point on the structure. A number of further retractable supports are provided underneath the awning to support the awning and are attached at one end to the structure.
U.S. Pat. No. 6,557,612 discloses a particular kind of articulated arm for supporting an awning, that can be extended and folded as the awning is extended and retracted.
Such systems that use a variety of arms, brackets and posts to support a cover have a number of disadvantages. Firstly, they can be bulky and heavy so that they can only be of a limited size and cover a relatively small area. This also means that they can be difficult and time consuming to erect and remove, which is obviously undesirable as a change in weather condition needs to be accommodated quickly. The supporting arms and brackets can be unattractive, but are required in known systems to support the cover and prevent it sagging, being particularly important with large covers.
Another system is known from French publication FR 2 559 527. The disclosed mechanism is designed for rolling up, unrolling and stretching an awning canopy over a horizontal or slightly sloping plane. The mechanism combines the rolling up, unrolling, traction and tension of a multi-purpose awning canopy. The rotation of a rolling-up tube unrolls the canopy and simultaneously rolls up (but in the opposite direction) a set of cables which, guided by two lateral pulleys and two return pulleys, pull a loading bar in which one or more traction springs are incorporated. These springs deliver a constant and progressive tension to the cables and to the canopy which is thus always stretched. At the end of the tube, a set of “ring pulleys” having a variable diameter, compensate for the various thicknesses of the rolled-up tube.
It can be seen that this system does not use large and heavy arms and brackets to support the cover, instead holding it taut and horizontal using two cables and providing tension with a spring. The cables must be thin enough to wrap round the small diameter of the ring pulleys. This system is not suitable for the heavy load of a large cover, not least because it relies on holding the cover in tension by the thin cables. Tension in the cover is also limited by the extent the spring can be stretched. Furthermore, the apparatus is limited by the tensile strength of the cover. Thus this system is clearly suitable only for small and light-weight covers with adequate tensile strength and is far from ideal for supporting large covers that require strong support and means to prevent sagging.
WO 2004/011760 describes a rolling blind in which two fabrics are wound conjointly on a keyway tube which travels along guide rails or wires, winding or unwinding both fabrics at once. The system provides tension in the fabrics by means of springs. This is one reason why it is not suitable for larger applications.